Incorporation of spectral sensitizing dyes or photographic dyes into silver halide photographic materials has prevailed in the field of silver halide photographic materials. In some cases, such dyes are observed as undesirable residual color because they still remain in silver halide photographic materials after the photographic materials are finished with image formation. Therefore, it is desirable that spectral sensitizing dyes or photographic dyes be completely removed from silver halide photographic materials or light absorption characteristics in the visible region will be lost after achievement of their purposes. As a means to remove such dyes or make the colors of such dyes disappear, the method of decolorizing a silver halide photographic material through elution of those dyes therefrom during the processing for image formation or the method of inducing the disappearance of colors in those dyes by the chemical reaction with a processing solution has so far been prevailingly employed. In recent years, however, the processing speed for image formation has been increased and the replenishment rates of processing solutions have been lowered; as a result, the means as mentioned above, which rely on the processing solutions used therein, sometimes have failed to completely remove the residual color ascribed to spectral sensitizing dyes or photographic dyes. Thus, measures to solve this problem have been sought.
There are known organic compounds of the kind which undergo reversible changes in their absorption wavelengths when the compound absorbs light of a particular wavelength. In general, these changes caused by light are referred to as photochromic reactions. Examples of an organic compound which is known to undergo a photochromic reaction include pyrenethioindigo, benzylviologen derivatives, benzospiropyran, spiroindolinonaphthoxazine, azobenzene and fulgide. These organic compounds generally exhibit reversible photochromic characteristics, and have a common feature that, even after they have undergone changes in their absorption wavelengths by irradiation with light, the absorption wavelengths thereof revert again to their original ones by exposure to heat or light. In cases where compounds of such a kind are added to silver halide photographic materials for the foregoing purpose, it is desirable that they undergo no or very slow recoloring reaction after the wavelength region in which they absorb light has once been shifted to a region other than the visible region, such as the ultraviolet or infrared region, by irradiation with light. If the irreversible decoloration of spectral sensitizing dyes or photographic dyes is achievable by irradiation with light during the image-forming processing, this irradiation means is very useful from the viewpoints of an increase in processing speed and a reduction in replenishment rate.
As examples of an organic compound which can undergo decoloration by applying thereto an energy such as heat, the cyanine dyes having alkoxy groups substituted on their nitrogen atoms have been proposed in, e.g., U.S. Pat. No. 3,745,009. However, those compounds have problems of stability and easiness in production, and the fact is that organic compounds having properties suitable for spectral sensitizing dyes or photographic dyes incorporated in silver halide photographic materials have not been obtained yet. Under these circumstances, it is strongly desired to find organic compounds which are stable upon storage, can rapidly cause irreversible decoloration or irreversible change in wavelengths at which they show absorption maxima by the absorption of light at particular wavelengths and, what is more, can be produced with ease, and silver halide photographic materials comprising those compounds as well.